Conventionally, an airflow-rate detecting device capable of detecting humidity is known to have a constitution as described in Patent Documents 1 and 2, or the like.
Patent Document 1 (JP 5178388 B2) describes an airflow-rate detecting device having a flow rate sensor and a humidity sensor. The flow rate sensor is disposed in an auxiliary air passage in which a part of intake air flows. The humidity sensor is disposed in a second auxiliary air passage that is open in the auxiliary air passage. That is, air flowing in the auxiliary air passage is branched on an upstream side of the flow rate sensor such that the flow rate sensor and the humidity sensor are disposed in different airflows.
However, in the flow rate detector of Patent Document 1, air turbulence causes, and accuracy of flow rate detection may decrease.
Patent Document 2 (JP 2013-036892 A) describes an airflow-rate detecting device having a housing, a flow rate sensor, and a humidity sensor. The housing has a bypass passage in which a part of intake air flows. The flow rate sensor is disposed in the bypass passage. The humidity sensor is disposed to protrude from the housing into a duct in which intake-air flows. Accordingly, a location of the humidity sensor may not have an effect on accuracy of flow rate detection.
However, in the flow rate detector of Patent Document 2, dust included in intake air adheres to the humidity sensor easily, and dust adhering to the humidity sensor may affect accuracy of flow rate detection.